TOKYO (Reuters) - Japanese trade minister Hiroshige Seko said on Tuesday that electricity supply will remain tight in Hokkaido in the wake of last week’s powerful earthquake until Friday, when the northern island’s utility is set to start operations at its Kyogoku No.2 pumped storage hydro power plant.

Hokkaido has been suffering power shortages since last Thursday’s major quake. Seko repeated calls on the island’s businesses and 5.3 million residents to use about 20 percent less electricity to prevent further blackouts.

Seko said the partial restart of a key coal-fired power plant damaged in the quake - which supplied about half of the island’s electricity before the temblor - is not expected before the end of September at the earliest.

The full restart of the plant’s three units, all of which have sustained damages, will be in November at the earliest, the minister said, adding the government has no plans for rolling blackouts in Hokkaido on Tuesday and Wednesday.